Mozilla’s web compatibility engineer has a clear message for Firefox users relying on the Chrome Mask extension: Don’t use it unless absolutely necessary.

The extension is designed to spoof Chrome’s user agent, helping users navigate sites that reject Firefox (likely because it doesn’t use Chromium). Some websites display “Unsupported browser” warnings; Chrome Mask makes them believe Firefox is actually Chrome.

It should only be used when required, such as university portals or workplace tools that don’t function properly in Firefox. The extension’s maintainer has advised users to leave it disabled for all other websites.

In a thread on Reddit, the web compatibility engineer (u/skyschub) explained that usage on websites such as YouTube triggers subtitles failure, aggressive CAPTCHA prompts, and erratic playback.

While some users report faster loading speeds, the maintainer says that any perceived gain in speeds usually stems from clearing the cache, and not the extension. You can just clear the browser cache on your own, without using Chrome Mask.

It was further emphasized that using Chrome Mask on sites that already support Firefox is counterproductive and can lead to bugs and issues. People using the extension go on to report these self-inflicted issues, which wastes the engineer’s time.

Hard-coding exceptions for Google domains to prevent the extension from being used beyond its intended purpose was considered. However, the idea was let out to avoid negative publicity and unreasonable online theories.

Beyond websites not functioning properly, there are broader risks. Masking Firefox usage in analytics diminishes the incentive for developers to address genuine compatibility issues. Many “Chrome-only” blocks are because of missing APIs; websites are not deliberately excluding Firefox.

All in all, the maintainer’s recommendation is to reserve Chrome Mask for websites that genuinely require it, and also to encourage direct fixes from developers.

In other Firefox news, there’s a classic arcade game hiding in plain sight. You can read about that here.

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